Embryology ,Anatomy and physiology of Larynx

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Embryology ,Anatomy and physiology of
Larynx

• Prepaired by
• Dr. Hiwa Asad Abdulkareem

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• Sources
• Scott-browns of otolaryngology , head and neck
  surgery .
• Synopsis of otolaryngology .
• www.drtbalu.com
• www.wekipedia.com

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Embryology of larynx

• Development of larynx
• during the 4th week of intra uterine life.
• starts in the form of laryngotracheal groove in
  the ventral wall of the pharynx.
• The groove gradually deepens and its edges fuse
  to form a septum, this septum separates the
  laryngotracheal tube from the pharynx and
  oesophagus.
• The process of this fusion starts caudally and
  extend cranially.

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• Lined with endoderm from which the epithelium of
  the airway develop.
• The cranial end of this laryngotracheal tube
  forms the larynx and the trachea.
• Caudally this tube produces two branches from
  which the two main bronchi develop.
• This is also the place from which the two lung
  buds starts to develop.
• Any congenital malformation of the pharynx
  and oesophagus is always
• associated with certain degree of
  malformation of larynx and trachea.

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• Primitive larynx is the cranial part of the
  laryngo tracheal groove.
• It is bounded by the caudal part of the
  hypobranchial eminence and laterally by the
  ventral folds of the sixth branchial arches.
• Epiglottis develops from the hypobranchial
  eminence.
• Arytenoid swellings appear on either side of the
  laryngo tracheal groove, as they enlarge they
  become approximated with each other and to the
  caudal portion of the hypobranchial eminence.
• This development converts the vertical slit of
  the laryngeal cavity into a T shaped one.
• Initially the walls of the cleft adhere to each
  other occluding the laryngeal cavity. During the
  third month of intrauterine life the lumen is
  restored by dissolution of the clump of cells
  occluding the cavity.

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• The nerves supplying the 4th and 6th arches
  (superior and recurrent laryngeal nerves supply
  the larynx)

Development of laryngeal cartilages Development of laryngeal cartilages
Developed from Name of the cartilage
Ventral ends of 4th arch cartilage Thyroid cartilage
6th arch Arytenoids
6th arch Corniculate
Hypobranchial eminence Epiglottis
6th branchial arch Cricoid Tracheal cartilages
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ANATOMY OF THE LARYNX

• Introduction
• Situated above the trachea.
• Extends from the laryngeal inlet to the inferior
  border of the cricoid cartilage .
• Opposite the third to sixth cervical vertebrae,
  being a little higher in women than in men.
• The infantile larynx
• Smaller than the adult compared to body size
• More funnel shaped.
• Its narrowest part is at the junction of the
  subglottic larynx with the trachea and even
  slight swelling in this area may result in marked
  airway obstruction .
• Cartilages are much softer and collapse more
  easily on forced inspiration.
• The larynx starts high up under the tongue in
  early life and with age assumes an increasingly
  lower position in the neck .

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• The size of the larynx is almost the same in boys
  and girls till puberty. After puberty the antero
  posterior diameter of the larynx virtually
  doubles in males .

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• The larynx is divided anatomically in to
• supra glottis .
• glottis . And
• sub glottis .
• By the falls and
• true vocal cords.

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• The supraglottis consists of superiorly the
• epiglottis and aryepiglottic folds as they sweep
  down to
• the arytenoids. Its lower border is the
  ventricular bands
• (false cords) which form the upper border of the
  glottis .
• The glottis includes the vocal cords and
  anterior
• commissure and posterior commissure.
• The sub glottis becomes the trachea at the lower
  border of the cricoid .( between true v.c . and
  lower border of the cricoid ) .

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The framework of the larynx

• Consists of
• hyoid bone
• number of cartilages
• connected by ligaments, membranes and intrinsic
  and extrinsic muscles to give it stability.
• They move in relation to one another by
• the action of the two groups of muscles.
• Lined with a mucous membrane
• that is continuous above with the pharynx
• and below with that of the trachea .

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• HYOID BONE
• U-shaped bone.
• Provides the upper attachment for many of the
  extrinsic muscles of the larynx.
• Suspends the larynx in the neck .

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• It consists of
• Body anteriorly
• Greater cornua project backwards on each side.
• Lesser cornua _two small conical eminences
  _attached to the upper part of the body of the
  hyoid by a fibrous band and sometimes to the
  greater cornua by way of a synovial joint .

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Cartilaginous skeleton of larynx

• 9 different cartilages present in the larynx .
• Unpaired cartilages
• (thyroid, cricoid , epiglottis)
• Paired cartilages
• (arytenoid , corniculate ,cuneiform)

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• THYROID CARTILAGE
• Thyroid cartilage
• Shield like.
• Largest of the laryngeal cartilages.
• Has two laminae meet in the midline inferiorly.
• The angle of fusion between the laminae is about
  90 degree in men and 120 degrees in women.
• The fused anterior borders in men form a
  projection, which can be easily palpated known as
  Adams apple.

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• The laminae diverge posteriorly.
• The posterior border of the two laminae are
  prolonged as two slender
• processes known as the superior and
  inferior cornua.

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• The Oblique Line
• The oblique line extends from the superior
  thryoid tubercle to the inferior thyroid
  tubercle.
• The oblique line gives attachment to the
  following muscles
• 1. Thyrohyoid muscle .
• 2. Sternohyoid muscle .
• 3. Inferior constrictor muscle .

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Ligaments attached to the thyroid cartilage

• Thyroepiglottic ligament elastic ligament
  connecting the epiglottis to the angle of the
  thyroid cartilage.
• Vestibular ligament Also known as the false
  vocal cord.
• Vocal ligament Also known as the true vocal cord
  is responsible for the generation of voice.

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CRICOID CARTILAGE

• The only complete cartilage ring in the whole of
  the respiratory pathway.
• Shaped like a signet ring.
• Composed of of a deep broad quadrilateral lamina
  posteriorly and a narrow arch anteriorly.

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• The lamina of the cricoid cartilage has
  articular facets for arytenoid cartilage . These
  joints are synovial in nature. The cricoid
  cartilage also articulates with the thyroid
  cartilage .

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THE ARYTENOID CARTILAGES

• Small paired cartilages placed close together on
  the upper and lateral borders of the cricoid
  lamina.
• Pyramidal shaped.
• Has two projections, forward and lateral
  projections.
• The forward projection is also known as vocal
  process. The vocal folds are attached to the
  vocal process.
• The lateral processes are also known as muscular
  process .

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• The apex of this cartilage curves backwards and
  articulates with corniculate cartilages.
  Aryepiglottic folds are attached to these
  cartilages.

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CORNICULATE AND CUNEIFORM CARTILAGES

• The corniculate cartilages are two small conical
  nodules of elastic fibrocartilage which
  articulate through a synovial joint with the
  apices of the arytenoid cartilages. They are
  situated in the posterior part of the
  aryepiglottic fold.
• The cuneiform cartilages are two small elongated
  flakes of fibroelastic cartilage, one in each
  margin of the aryepiglottic fold.

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EPIGLOTTIS

• Leaf shaped fibroelastic cartilage .
• Projects upwards behind the tongue and the body
  of the hyoid bone.
• Its upper part is broad and is directed upwards
  and backwards.
• Superior margin is free.
• The sides of the epiglottis is attached to the
  arytenoid cartilages by aryepiglottic folds.

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• The anterior surface of the epiglottis is free
  and is covered with the same mucous membrane
  which is of the of pharynx.
• Forms a single median glossoepiglottic fold and
  two lateral glossoepiglottic folds.
• Between these folds lie a depression known as the
  vallecula.
• In neonates and infants the epiglottis is omega
  shaped.
• This long, deeply grooved, floppy epiglottis
  protects the nasotracheal air passage during
  sucking.

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Laryngeal joints

• Crico-thyroid joint between thyroid and cricoid
  cartilages. Its a synovial joint.
• Tow movements occur
• Rotation through a transverse axis .
• Gliding , slightly .

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• Crico- arytenoid joint
• Between arytenoid and the cricoid cartilage .
  Its a synovial joint.
• Tow movements occur
• Rotation .of the arytenoid , on vertical axis .
  The vocal process moves medially or laterally .
• Gliding . the arytenoid moves toward or away from
  each other .

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Ligaments and membranes of the larynx

• Extrinsic and Intrinsic ligaments .
• Extrinsic ligaments connect the laryngeal
  cartilages to the hyoid bone above
• and
  trachea below.
• Thyro-hyoid membrane between the upper border
  of the thyroid and the the body and greater
  cornua of the hyoid bone.

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• Crico-tracheal ligament Unites the lower border
  of the cricoid cartilage with the first tracheal
  ring .
• Hyo-epiglottic ligament connects the epiglottis
  to the back of the body of the hyoid bone.

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• Intrinsic ligaments
• ligaments that connect the laryngeal cartilages.
  
• Strengthen the capsule of intercartilagenous
  joints.
• Form a broad sheet of fibroelastic tissue which
  lie beneath the mucous membrane of the larynx
  creating an internal framework .

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• The fibroelastic membrane
• Divided into
• upper and lower part by the presence of
  laryngeal ventricle.
• The upper membrane is the quadrilateral
  membrane.
• It extends between epiglottis and the arytenoid
  cartilage.
• Its upper margin forms a framework for the
  aryepiglottic fold.
• Its lower margin is thickened to form the
  vestibular ligament, which underlies the
  vestibular fold or false vocal cord.

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• The lower part is a thicker membrane,
  containing many elastic fibers. It is also known
  as cricovocal ligament or cricothryoid ligament
  or conus elasticus.
• Below it is attached to the upper border of the
  cricoid cartilage.
• Above it is stretched between the midpoint of
  thyroid cartilage anteriorly and the vocal
  process of the arytenoid behind.
• The free upper border of this membrane forms the
  vocal cord.

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Muscles of the larynx

• The extrinsic muscles .
• intrinsic muscles .

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extrinsic muscles of the larynx

• connect the laryngeal cartilages to
• Hyoid bone above and trachea below .
• and maintain the position of the
• larynx in the neck .
• Divided Into
• Infra hyoid group ( strap muscles )
• ( Thyrohyoid , Sternothyroid ,
• Sternohyoid , omohyoid ) .
• Supra hyoid group
• ( Mylohyoid , Geniohyoid, Stylohyoid ,
• Digastric , Stylopharyngeus ,
• Palatopharyngeus , Salpingopharyngeus (

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• Fig. show strap muscles of the neck

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• All of the infrahyoid muscles are innervated by
  the ansa cervicalis from the cervical
  plexus (c1-c3 ) except the thyrohyoid muscle,
  which is innervated by fibres only from the 1st
  cervical signal nerve travelling with the
  hypoglosal nerve .

Action Insertion origin muscle
draws the larynx downwards . lower edge of the body of the hyoid posterir surface of the manubrium sterni and the 1st costal cartilage Sterno hyoid
rises the larynx if the hyoid is fixed . Depress the hyoid if the larynx is fixed . lower border of the greater horn of the hyoid bone oblique line on the thyroid ala Thyrohyoid
Depresses the larynx oblique line on the thyroid lamina . posterir surface of the manubrium and the 1st costal cartilage Sternothyroid
Depresses the larynx intermediate tendon superior border of scapula omohyoid (inferior belly )
Depresses the larynx Lateral surface of hyoid bone intermediate tendon omohyoid (superior belly )
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• Suprahyoid group

inervation Action Insertion origin muscle
Nerve to mylohyoid (inferior alveolar branch of v3 ) Raises and pulls the hyoid . Midline raphe and body of hyoid . Mylohyoid line on the inner aspect of Mndible . Mylohyoid
Hypoglossal (C1 root) Raises and pulls the hyoid forward . Upper border of the body of hyoid . Genial tubercle on Mndible . Geniohyoid
Facial nerve . Retractor and elevator of hyoid for swallowing . Base of greater cornu of thyroid . Back of the styloid (split around digastric process ) Stylohyoid
Posterior belly facial nerve . Anterior belly - nerve to mylohyoid . Anterior belly pulls the Hyoid anterior and up . posterior belly pulls Hyoid post. and up. Lower border of the Mandible .fibrous sling holds the tendon to lesser cornu of hyoid . Digastric notch on the medial surface Mastoid process . Digastric
Glossopharyngeal nerve Elevates the larynx post. Border of lamina of th. Cart.( side wall Of pharynx ) Medial aspect of the styloid process . Stylopharyngeous
Accessory nerve pharyngeal plexus)) Helps tilts the larynx forward . post . Border of thyroid alar and cornu. Palatine aponeurosis And post. Margin of palat . Palatopharyngeus
Pharyngeal plexus Elevates the larynx post . Border of thyroid cart. .( side wall of pharynx ) Eustachian tube Salpingopharyngeus
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Intrinsic muscles of larynx

• The intrinsic muscles are all paired and move the
  cartilages in the larynx and regulate the
  mechanical properties of the larynx. They control
  the position and shape of the vocal
• folds and control the elasticity and viscosity
  of each layer .

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• Divided into
• Open and close the glottis(lateral and posterior
  cricoarytenoid muscles, transverse and oblique
  arytenoids).
• Control the tension of vocal ligaments
  (thyroarytenoids, vocalis and cricothyroids).
• Alter the shape of the inlet of the larynx
  (aryepiglotticus and the thyroepiglotticus).
• Except transverse arytenoid,
  all these muscles are paired.
• Abductor of vocal cords there is only one each
  side .
• Posterior cricoarytenoid muscle is the only
  muscle that opens the glottis, separating the
  vocal processes and thus abducts the vocal cords.
  

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• Adductors of vocal cords three on each side .
• Lateral cricoarytenoid muscle
• Adducts the vocal ligaments by
  rotating the arytenoids medially.

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• Transvers portion of inter arytenoid muscle
• A single muscle.
• Adduct the vocal cord .

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• External portion of thyroarytenoid muscle
• A thin sheet which lies out side the vocal cord ,
  venticle and saccule of the larynx .
• It closes the rima glottis by medial rotation of
  Arytenoid cartilage around longitudinal axis .

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• Tensors of the vocal cords 2 on each side .
• cricothyroid muscle
• The only intrinsic muscle that lie outside the
  cartilaginuos framework of the larynx .
• It is known as the External tensor .

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• Internal portion of thyro- arytenoid ( vocalis )
  m.
• A specialized portion of the lower and
  deeper fibers of the thyro-arytenoid muscle .
• It forms a triangular bundle.
• Some of its fibers gain its attachment to the
  vocal ligament.
• It is known as the internal tensor .

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• Opener of laryngeal inlet
• Fibers of thyro-epiglottic muscle is apart of the
  thyro-arytenoid muscle widens the inlet of the
  larynx by pulling the ary-epiglottic folds
  slightly apart .

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• Closers of the laryngeal inlet
• Oblique portion of inter-arytenoid muscle is
  superficial to the transvers portion . The two
  bundle of fibers cross each other closes the
  rima glttis .
• Ary-epiglotic muscle is prolongation of the
  oblique fibers of inter- arytenoid muscle
• in to the ary- epiglotic fold .
• All intrinsic muscles of the larynx are supplied
  by recurren laryngeal nerve except
• Crico-thyroid m. which is supplied by external
  laryngeal nerve ..

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• Interior of larynx
• The laryngeal cavity extends from the level of
  3rd cervical vertebra to the lower border of the
  cricoid cartilage (c6) level. At the level of
  cricoid cartilage it becomes continuous with that
  of the trachea.

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• Laryngeal cavity is divided by the presence of
  vestibular and vocal folds into
• Larynx above the vestibular fold is known as
  superior vestibule.
• The ventricle or sinus of the larynx lies between
  the vestibular and vocal folds.
• Below the vocal folds is the subglottic space
  which extends to the level of the lower border of
  the cricoid cartilage.

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• False vocal cord ( the ventricular bands) which
  are formed by the mucous membrane covering the
  ventricular ligament and the upper part of the
  external portion of the thyroarytenoid muscle.
• True vocal cords Project further into than the
  false cords, and
• lie at a lower level. The covering epithelium
  is closely bound down to the underlying vocal
  ligament. The blood supply is poor, hence the
  pearly white appearance of the vocal cords.

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• Histologically the vocal fold
• contains 5 layers
• Layer 1 (squamous epithelial lining) It is very
  thin .
• Layer 2 (Superfical layer of the lamina propria
  Reinke's space ) composed of loose fibers and
  matrix.. This layer contains only minimal elastic
  and collagenous fibers and offers least
  resistance to vibration. The integrity of this
  layer is vital for proper phonatory function.
• Layer 3 (Intermediate layer of lamina propria)
  a higher concentration of elastic and collagenous
  fibres. Provides protection to the vocal folds
  from mechanical damage.
• Layer 4 (Deep layer of lamina propria) a dense
  collection of elastic and collagenous fibers.
• Along with the intermediate layer
  constitute the vocal ligament.
• Layer 5 (vocalis muscle) portion of thyro
  _arytenoid muscle.

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• Fig showing ultra structure of vocal cord

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• Vestibule Lies between the laryngeal inlet and
  the edges of the false cords.
• Bounderies
• Posterior surface of epiglottis in front.
• Interval between the arytenoid cartilages behind.
  
• Inner surface of the aryepiglottic folds and
  upper surfaces of the false cords on each side.

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• Laryngeal inlet is bounded
• superiorly by the free edge of epiglottis
• and on each side by the aryepiglottic folds.
• Posteriorly by the mucous membrane between the
  arytenoid cartilages.

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• Mucous membranes of the larynx
• Most of the larynx is lined by pseudo stratified
  ciliated columnar 'respiratory' -type epithelium.
  
• The upper half of the posterior surface of the
  epiglottis, the upper part of the aryepiglottic
  fold, the posterior glottis and the vocal folds
  are covered with nonkeratinizing stratified
  squamous epithelium.
• Mucous glands are freely distributed throughout
  the mucous membranes and are particularly
  numerous on the posterior surface of the
  epiglottis and in the margins of the lower part
  of the aryepiglottic folds and in the saccules.
• The vocal folds do not possess any glands and the
  mucous membrane is lubricated by mucus from the
  glands within the saccules.
• The squamous epethelium of the vocal folds is
  therefor Pron to desiccation if these glands
  cease to function, for example after radiation .

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• Ventricle of larynx
• between the vestibular and vocal folds, overlie
  the ligaments of the same name.
• On each side the laryngeal ventricle opens into
  an elongated recess known as the laryngeal sinus.
  
• From the anterior part of the ventricle, a pouch
  called the saccule of the larynx ascends between
  the vestibular folds and the inner surface of the
  thyroid cartilage.
• The mucous membrane of saccule contains numerous
  mucous secreting glands. These secretions
  lubricates the vocal cord.

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• Rima glottis is an elongated fissure present
  between the two vocal folds.
• Rima vestibuli The rima vestibuli is the
  triangular-shaped opening between the 2 adjacent
  vestibular folds.

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• Pyriform recesses
• The pyriform recesses (pyriform sinuses) are
  present on either side of the anterolateral wall
  of the laryngopharynx. They are bounded medially
  by the aryepiglottic folds and laterally by the
  thyroid cartilage and thyrohyoid membrane. They
  are a common place for food to become trapped.

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• Spaces within the larynx
• Preepiglottic space Is a wedge shaped space
  lying in front of the epiglottis. It is bounded
  anteriorly by the thyrohyoid ligament and the
  hyoid bone. This space is continuous laterally
  with that of paraglottic space. Tumour may spread
  into this area through small perforations in the
  epiglottis or directly through, the hyoepiglottic
  ligament.

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• Paraglottic space is a potential space present
  on either side of glottis. It is bounded by the
  mucosa covering the lamina of thyroid cartilage
  laterally, the conus elasticus and quadrangular
  membranes medially and the anterior reflection of
  the pyriform fossa mucosa posteriorly .

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Blood supply of the larynx Is derived from the

• laryngeal branches of the superior thyroid
  arteriy . .
• laryngeal branches of the inferior thyroid
  arteriy .
• the cricothryoid branch of the superior thyroid
  artery.
• The superior thyroid artery arises from the
  external carotid artery, and the inferior thyroid
  artery arises from the thyrocervical trunk.
• The veins leaving the larynx accompany the
  arteries
• The superior vessels drain to the internal
  jugular vein by
• way of the superior thyroid or facial veins ,
• The inferior vessels drain by way of inferior
  thyroid vein
• into the brachiocephalic veins.
• Some venous drainage also occur
• through the middle thyroid vein into the internal
  jugular vein.

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• Lymphatic drainage
• Separated by the vocal folds into an upper and
  lower group
• The part of the larynx above the vocal folds is
  drained by vessels accompanying the superior
  laryngeal vein,
• The zone below the vocal folds drains together
  with the inferior vein, into the lower part of
  the deep cervical chain often through the
  prelaryngeal and pretracheal nodes.
• The vocal folds are devoid of lymphatics, and it
  infact clearly forms the watershed zone between
  the upper and the lower group of lymphatics.

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• Nerve supply of the larynx
• The larynx is supplied by branches of vagus nerve
  .
• Superior laryngeal nerve has two laryngeal
  branches
• Internal branch . Entirly sensory . It pierces
  the thyrohyoid membrane with the
• superior laryngeal artery and vien . It supplies
  the cavity of the larynx as far down
• the level of the vocal cords .
• External branch . Travels down on the inferior
  constrictor muscle of the pharynx . It supplies
  the cricothyroid muscle and part of the ant.
  Subglottis .

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• Recurrent laryngeal branch of the vagus nerve (CN
  X)
• It has much longer course on the left side than
  on the right side .
• On the lt. side it Turns round the arch of
  aorta .
• On the rt. Side it Turns round the subclavian
  artery.
• In the neck it lies between the trachea and
  oesophagus as it approach the larynx .
• Its terminal part pass upwards , under cover of
  ala of the thyroid cartilage , immidiately
  behind the cricothyroid joint .
• Devided In to
• An antero lateral ( motor branch ) which supply
  all the intrinsic ms. Of the larynx except the
  cricothyroid m.
• Posteromedial ( sensory branch) which
  supplies the cavity of the larynx below the level
  of vocal cords .

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Physiology of  Larynx
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Functions of larynx

• 1. Airway protection
• 2. Respiration
• 3. Swallowing
• 4. Coghing
• 5. phonation

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• Airway protection
• The most important function of human larynx. 
• A sphincter protecting the lower airway from
  secretions of oropharynx.
• Protects the airway from spillage of food during
  deglutition.
• Larynx has three protective mechanisms (from
  above downwards)
• Aryepiglottic fold, ventricular
  band and vocal cords.

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• Respiration
• Larynx is part of the upper airway passages .
• keeps the airway open during respiration.
• Contributes to the regulation of the acid-base
  balance in the blood by influencing CO 2 tension
  .

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• Swallowing 
• During swallowing the sphincters of larynx stay
  contracted preventing aspiration of food into the
  air passage.

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• Coughing
• Coughing is the process by which material is
  expelled
• from the airway.
• It is preceded by rapid inspiration, followed by
  forceful closure of both the vocal and vestibular
  folds.
• Air pressure is then built up below the adducted
  folds.
• The diaphragm ascends spasmodically until the
  folds separate explosively and mucus or foreign
  material is expelled.

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• Phonation
•   The larynx acts as a transducer during
  phonation converting the aerodynamic forces
  generated by the lungs, diaphragm, chest and
  abdominal muscles into acoustic energy.
• The requirements of normal phonation are as
  follows
• 1. Active respiratory support
• 2. Adequate glottic closure
• 3. Normal mucosal covering of the vocal cord
• 4. Adequate control of vocal fold length and
  tension.

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• The cycle of sound production involves glottic
  opening and closing at set frequencies determined
  by the subglottic air pressure.
• The function of vocal folds is to produce sound
  varying in intensity and pitch. This sound is
  then modified by various resonating chambers
  present above and below the larynx and are
  converted into words by the articulating action
  of the pharynx, tongue, palate, teeth and lips.

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Thanks